Method of electrochemically fabricating multilayer structures having improved interlayer adhesion

Abstract

Multi-layer microscale or mesoscale structures are fabricated with adhered layers (e.g. layers that are bonded together upon deposition of successive layers to previous layers) and are then subjected to a heat treatment operation that enhances the interlayer adhesion significantly. The heat treatment operation is believed to result in diffusion of material across the layer boundaries and associated enhancement in adhesion (i.e. diffusion bonding). Interlayer adhesion and maybe intra-layer cohesion may be enhanced by heat treating in the presence of a reducing atmosphere that may help remove weaker oxides from surfaces or even from internal portions of layers.

1 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer of material to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least twice to build up a three-dimensional structure from a plurality of adhered layers, wherein the desired patterning on at least two layers is different;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment;    wherein the structure comprises at least one metal, and wherein formation of the desired pattern for at least one layer comprises use of an adhered mask.    
   
   
       2 . The process of  claim 1  wherein the forming and adhering for at least two layers comprises electrodepositing the at least one metal.  
   
   
       3 . The process of  claim 2  wherein the heat treatment results in improvement of adhesion strength between metal deposits.  
   
   
       4 . The process of  claim 1  wherein the electrodepositing comprises electroplating the at least one metal.  
   
   
       5 . The process of  claim 4  wherein the heat treatment results in improvement of adhesion strength between metal deposits.  
   
   
       6 . The process of  claim 2  wherein the at least one metal comprises nickel.  
   
   
       7 . The process of  claim 1  wherein each of a plurality of layers comprises at least two metals, wherein at least one of the metals is a sacrificial material and at least one other metal is a structural material that forms at least part of the structure.  
   
   
       8 . The process of  claim 7  wherein the sacrificial material comprises copper.  
   
   
       9 . The process of  claim 7  wherein the structural material comprises nickel.  
   
   
       10 . The process of  claim 3  wherein the adhesion strength increases by at least a factor of about two.  
   
   
       11 . The process of  claim 10  wherein the adhesion strength increases by at least a factor of about five.  
   
   
       12 . The process of  claim 1  wherein the heat treatment comprises heating the structure at more than about 250° C. for at least one hour.  
   
   
       13 . The process of  claim 12  wherein the heat treatment comprises heating of the structure to more than about 250° C. for at least three hours.  
   
   
       14 . The process of  claim 1  wherein the heat treatment comprises heating the structure at more than 200° C. for no more than two hours.  
   
   
       15 . The process of  claim 14  wherein an atmosphere comprising a reducing gas is located around the structure while a temperature of the structure is greater than about 200° C.  
   
   
       16 . The process of  claim 14  wherein an atmosphere comprising a reducing gas is located around the structure while a temperature of the structure is greater than about 100° C.  
   
   
       17 . The process of  claim 1  wherein the heat treatment comprises heating the structure at more than 200° C. for no more than one hour.  
   
   
       18 . The process of  claim 17  wherein an atmosphere comprising a reducing gas is located around the structure while a temperature of the structure is greater than about 200° C.  
   
   
       19 . The process of  claim 17  wherein an atmosphere comprising a reducing gas is located around the structure while a temperature of the structure is greater than about 100° C.  
   
   
       20 . The process of  claim 1  where the improvement in adhesion strength results at least in part from heat-aided material diffusion across a boundary where a later deposition joins a surface of a previously deposited material.  
   
   
       21 . The process of  claim 1  wherein the formation of a layer additionally comprises the planarization of deposited material.  
   
   
       22 . The process of  claim 7  wherein the heat treatment occurs prior to a release of the sacrificial material from the structural material.  
   
   
       23 . The process of  claim 1  wherein the formation of at least a plurality of layers, comprises beginning a deposition operation to form a portion of a subsequent layer prior to completing formation of a previous layer.  
   
   
       24 . A process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming a patterned deposit of at least one first material on to a substrate or previously deposited material such that at least one void exists around or within the patterned deposit of the at least first material;    (b) depositing at least one second material into at least a portion of the at least one void;    (c) trimming the deposit of at least on of the at least one first material or the at least one second material to a desired level;    (d) repeating the forming and adhering operations of (a)-(c) a plurality of times to build up a three-dimensional structure from a plurality of adhered layers;    (e) after formation of at least a plurality of layers, subjecting the multi-layer structure to heat treatment,    wherein at least one deposited material comprises a metal, and wherein the formaitng of the patterned deposit for at least one layer comprises use of an adhered mask.    
   
   
       25 . The process of  claim 24  wherein the heat treatment results in an increase in the adhesion between at least a portion of the overlaying depositions of at least one of the first and/or at least one of the second deposited materials.  
   
   
       26 . The process of  claim 25  wherein the enhanced adhesion results, at least in part, from heat-aided diffusion of material across a boundary joining two deposits.  
   
   
       27 . The process of  claim 1  wherein the heat treatment occurs with a ratio of pressure along an axis perpendicular to a plane of the layers to that exerted along an axis parallel to the planes of the layers which is no greater than about 10.  
   
   
       28 . The process of  27  wherein the ratio is no greater than about 2.  
   
   
       29 . The process of  claim 28  wherein the ratio is substantially 1.  
   
   
       30 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers, wherein at least a plurality of the layers each comprise at least two deposited materials;    (c) after formation of at least a plurality of layers and while at least two materials remain in contact adhered to one another, subjecting the multi-layer structure to a heat treatment;    wherein the structure comprises at least one metal.    
   
   
       31 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers, wherein the forming of at least a plurality of layers comprises removing at least some deposited material in a planarization operation;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment;    wherein the structure comprises at least one metal, and wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       32 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers, wherein the desired patterning of at least one material deposited on a subsequent layer adheres directly to the desired patterning of at least one material deposited on a preceding layer;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment;    wherein the structure comprises at least one metal, and wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       33 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment, wherein the structure is heated in a manner such that any local temperature variations within the structure do not directly result from localized differences in electrical conductivity of the structural material;    wherein the structure comprises at least one metal, and wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       34 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment such that substantially all portions of the structure are heated to a substantially uniform temperature;    wherein the structure comprises at least one metal.    
   
   
       35 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment, wherein a maximum temperature during heat treatment is less than a recrystallization temperature of at least one metal forming part of the structure, and    wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       36 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers, wherein at least a plurality of the layers each comprise at least one structural material and at least one sacrificial material;    (c) separating the sacrificial material from the structure to release the structure; and    (d) after formation of at least a plurality of layers but prior to release, subjecting the multi-layer structure to a heat treatment;    wherein the structure comprises at least one metal, and wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       37 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers, wherein at least a plurality of the layers each comprise at least one structural material and at least one sacrificial material, and wherein the desired patterning on at least two layers is different;    (c) separating the sacrificial material from the structure to release the structure; and    (d) after release, subjecting the multi-layer structure to a heat treatment;    wherein the structure comprises at least one metal, and wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       38 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) subjecting the multi-layer structure to a heat treatment while the structure is located in a selected atmosphere comprising an inert gas,    wherein the structure comprises at least one metal.    
   
   
       39 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) subjecting the multi-layer structure to a heat treatment while the structure is located in a selected atmosphere comprising a reducing gas,    wherein the structure comprises at least one metal.    
   
   
       40 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers, wherein at least a plurality of the layers each comprise at least one structural material and at least one sacrificial material, and wherein the desired patterning on at least two layers is different;    (c) separating the sacrificial material from the structure to release the structure;    (d) after release, subjecting the multi-layer structure to a heat treatment;    (e) after the heat treatment, applying a second sacrificial material to the structure.    wherein the structure comprises at least one metal.    
   
   
       41 . The fabrication process of  claim 40  the second sacrificial material comprises a material that is different from the at least one sacrificial material which comprised a portion of the layers.  
   
   
       42 . The fabrication process of  claim 40  the second sacrificial material comprises at least one material that is substantially the same as the at least one sacrificial material which comprised a portion of the layers.  
   
   
       43 . The fabrication process of  claim 40  the second sacrificial material is removed.  
   
   
       44 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer of material to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least twice to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment; and    (d) releasing the structure from the substrate,    wherein the structure comprises at least one metal, and wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       45 . The fabrication process of  claim 44  wherein the structure is released from the substrate prior to heat treatment.  
   
   
       46 . The fabrication process of  claim 44  wherein the structure is released from the substrate after heat treatment.  
   
   
       47 . A fabrication process for forming a multiple multi-layer three-dimensional structures, comprising: 
 (a) forming and adhering a layer of material to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least twice to build up a plurality of three-dimensional structures from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment; and    (d) dicing the plurality of structures from one another,    wherein the structure comprises at least one metal.    
   
   
       48 . The fabrication process of  claim 47  wherein the dicing occurs in at least two steps, one of which results in partial dicing prior to heat treatment, and another of which results in the completion of dicing after heat treatment.  
   
   
       49 . The fabrication process of  claim 47  wherein the dicing is completed prior to heat treatment.  
   
   
       50 . The fabrication process of  claim 47  wherein the dicing is completed after heat treatment.  
   
   
       51 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment, wherein a maximum effective temperature during heat treatment is less than a recrystallization temperature of at least one metal forming part of the structure, and wherein the heat treatment is applied for a sufficient time and at a sufficient temperature and in an environment that allows interlayer adhesion to be enhanced a substantial amount, and    wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       52 . The process of  claim 51  wherein the substantial amount comprises at least a factor of two.  
   
   
       53 . The process of  claim 51  wherein the substantial amount comprises at least a factor of five.  
   
   
       54 . The process of  claim 51  wherein the substantial amount corresponds to the interlayer adhesion strength being greater than about 50% of the yield strength of the interlayer material.  
   
   
       55 . The process of  claim 51  wherein the substantial amount corresponds to the interlayer adhesion strength being greater than about the yield strength of the interlayer material.  
   
   
       56 . The process of  claim 51  wherein the substantial amount corresponds to the interlayer adhesion strength being greater than about 50% of the ultimate tensile strength of the intra-layer material.  
   
   
       57 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment, wherein the heat treatment is applied to the structure for a temperature, a time, and in an environment such that a substantial increase in interlayer adhesion results without significantly reducing the yield strength of the intra-layer material, and    wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       58 . The process of  claim 57  wherein the substantial increase comprises at least a factor of two and the reducing is no more than 50% of the yield strength prior to heat treatment.  
   
   
       59 . The process of  claim 57  wherein the substantial amount comprises at least a factor of five and the reducing is no more than 75% of the yield strength prior to heat treatment.  
   
   
       60 . The process of  claim 57  wherein the substantial amount corresponds to the interlayer adhesion strength being greater than about 50% of the yield strength prior to heat treatment and the yield strength after heat treatment is no less than 75% of the yield strength prior to heat treatment.  
   
   
       61 . The process of  claim 57  wherein the substantial amount corresponds to the interlayer adhesion strength being greater than about the yield strength after heat treatment and the yield strength after heat treatment being no less than 75% of its value prior to heat treatment.  
   
   
       62 . The process of  claim 57  wherein the substantial amount corresponds to the interlayer adhesion strength being greater than about 50% of the ultimate tensile strength of the intra-layer material and the ultimate tensile strength of the interlayer material being no less than 75% of its value prior to heat treatment.  
   
   
       63 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment, wherein the heat treatment results in the formation of a structure which behaves monolithically up to at least 50% of the yield strength of the intra-layer material, and wherein the forming and adhering of at least one layer comprises use of an adhered mask in the selective patterning of at least one material.    
   
   
       64 . The process of  claim 63  wherein yield strength of the intra-layer material is that of the intra-layer material prior to heat treatment.  
   
   
       65 . The process of  claim 63  wherein yield strength of the intra-layer material is that of the intra-layer material after heat treatment.  
   
   
       66 . The process of  claim 63  wherein monolithic behavior exists when stresses are at or below 50% of the yield strength of the intra-layer material and inter-layer adhesion failure is no more likely to occur than intra-layer cohesion failure.  
   
   
       67 . The process of  claim 63  wherein monolithic behavior exists when stresses are at or below about 50% of the ultimate yield strength of the intra-layer.  
   
   
       68 . The process of  claim 67  wherein yield strength of the intra-layer material is that of the intra-layer material prior to heat treatment.  
   
   
       69 . The process of  claim 67  wherein yield strength of the intra-layer material is that of the intra-layer material after heat treatment.  
   
   
       70 . A fabrication process for forming a multi-layer three-dimensional structure, comprising: 
 (a) forming and adhering a layer to a previously formed layer and/or to a substrate, wherein the layer comprises a desired pattern of at least one material; and    (b) repeating the forming and adhering operation of (a) at least once to build up a three-dimensional structure from a plurality of adhered layers;    (c) after formation of at least a plurality of layers, subjecting the multi-layer structure to a heat treatment, wherein the heat treatment results in the formation of a structure which is no more likely to experience interlayer adhesion failure than intra-layer cohesion failure when applied stress is at least 50% of the yield strength of the intra-layer material.    
   
   
       71 . The process of  claim 70  wherein yield strength of the intra-layer material is that of the intra-layer material prior to heat treatment.  
   
   
       72 . The process of  claim 70  wherein yield strength of the intra-layer material is that of the intra-layer material after heat treatment.